From the Sixth Street Bridge, there's a fine view of the fierce pink sunset over downtown Los Angeles, but Edgar Juarez is interested only in the tarmac. It's a warm evening in early September, and Juarez, a 29-year-old electrician from Long Beach, California, is preparing to take part in the second annual Wolfpack Hustle Midnight Drag Race.

In 2007 a long-lost suitcase, forgotten for over half a century in the house of a retired general in Mexico, was found to contain 4,000 photographs of the Spanish Civil War. Many of them were by Robert Capa, the most famous war photographer of the 20th century. The existence of the suitcase had been rumoured since it disappeared in 1940, at the time of the Nazi invasion of France, but the survival of its contents seemed unlikely. In terms of shoc...